SegWit

Segregated Witness, or SegWit, is the name used for an implemented soft fork change in the transaction format of Bitcoin. The formal title "Segregated Witness (Consensus layer)" had Bitcoin Improvement Proposal number BIP141. The declared purpose was to prevent nonintentional bitcoin transaction malleability, allow optional data transmission, and to bypass certain protocol restrictions (such as the block size limit) with a soft fork. It was also intended to mitigate a blockchain size limitation problem that reduces bitcoin transaction speed. It does this by splitting the transaction into two segments, removing the unlocking signature ("witness" data) from the original portion and appending it as a separate structure at the end. The original section would continue to hold the sender and receiver data, and the new "witness" structure would contain scripts and signatures. The original data segment would be counted normally, but the "witness" segment would, in effect, be counted as a quarter of its real size. Bitcoin is a cryptocurrency, a form of currency using cryptography to keep transactions secure. A collection of bitcoin transactions prefaced by a block header, protected by proof of work, and recorded on a network of computers is called a "block". All blocks are tied together sequentially by using a cryptographic hash on the previous block and storing its output in the next. This forms a blockchain. Each block contains information about who sends and receives a given unit of bitcoin (a transaction), as well as the signature(s) that approves each transaction. Originally, there was no limit to the size of blocks. However, this allowed malicious actors to make up fake "block" data that was very long as a form of denial-of-service attack (DoS attack). These fake blocks would be detected, but doing so would take a very long time, slowing down the whole system. Therefore, a block size limit of 1 MB was introduced. The current bitcoin blockchain design is regarded as having two shortcomings.